Electric discharge tube



ay 1937. J. G. w. MULDER ELECTRIC DISCHARGE TUBE Filed Jan. 8, 1929 Patented May 25, 1937 UNITED STATES PATENT OFFICE ELECTRIC DISCHARGE TUBE Netherlands Application January 8, 1929, Serial No. 331,122 Inthe Netherlands March'9, 1928 4 Claims.

This invention relates to an electric discharge tube, which comprises an incandescent cathode and a gaseous filling and which is adapted for rectifying multiphase alternating current.

With rectifying valves comprising a gaseous filling, difficulty is encountered if the pressure of the gaseous filling is low, which is particularly the case with high voltage valves. In this case a heavy disintegration occurs in the metal parts arranged within the discharge space, this disintegration being accompanied by an absorption of a quantity of the gas enclosed within the tube. As a result of this absorption, the pressure in the valve decreases and the rectifier may be deleteriously affected and may even become unsuited for use. The presence of a quantity of mercury in the valve may practically prevent a decrease in pressure as a result of gas absorption. In this case, however, the phenomenon often occurs in multiphase rectifier valves that the discharge to one of the anodes is not struck.

The invention has for its object a discharge tube or thermionic valve for rectifying multiphase alternating current at a low gaseous pressure in which, in spite of the occurrence of any disintegration, the pressure does not decrease during operation, and in which the ignition does not present the above difficulty.

An electric discharge tube according to the invention comprising an incandescent cathode (preferably an oxide cathode) and a gaseous filling is adapted for rectifying multiphase alternating current. It is characterized by the presence in the evacuated space of mercury vapour mixed or not mixed with another gas, and liquid mercury. The incandescent cathode and the anodes have arranged between them, either outside on the tube wall or in the interior of the tube, one or more conducting members which in both cases are electrically connected to the corresponding anode, in the latter case preferably with the interposition of a condenser.

The liquid mercury may be enclosed within a separate reservoir which communicates with the interior of the tube preferably through a capillary tube.

This mercury reservoir may be arranged within a stem sealed to the tube.

A particular construction of the tube embodying the invention comprises means to permit the temperature of the mercury reservoir to be controlled.

The invention will be more clearly understood by reference to the accompanying drawing in which two constructions of a discharge tube embodying the invention are illustrated.

Figure 1 is a section of a multiphase rectifier with a reservoir for liquid mercury.

Figure 2 is a section of a multiphase rectifier 5 with another arrangement of the cathode, the mercury reservoir and the metal members between anodes and cathode.

Figure 3 is a section of a multiphase rectifier substantially corresponding with Figure 2, but wherein the corresponding members are placed within the tube.

Referring to Figure 1, a glass envelope l is sealed by a stem 2, the pinch 3 of which has sealed in it lead wires supporting an incandescent cathode 4. Each of the anodes 5, the number of which corresponds to the number of phases to be rectified, are enclosed in an arm 6 communicating with the discharge space. The arms 6, two of which are shown in the figure, may be arranged 0 outside the envelope l or inside, for example on one or more stems.

A reservoir 1, which contains mercury, communicates with the tube 1 through a capillary tube 8. The evacuated space of the tube will thus be filled with mercury vapour, the pressure of which depends upon the temperature of the mercury within the reservoir 1, provided this temperature is lower than that of the tube. As the said temperature is substantially constant, the pressure in the tube will remain practically constant even during operation. If the tube contains,in addition to mercury vapour another gas,

for example argon, the pressure will nevertheless be less dependent upon gas absorption than if the tube did not contain mercury. Alternatively, the

mercury may be provided in the tube as a liquid, for example, as a coating on the wall, and even in this case the pressure in the tube will be practically constant. However, a separate reservoir has great advantages over the last-mentioned method. By connecting the reservoir to the main tube through a capillary tube, the liquid mercury remains entirely separated from the tube and cannot come into contact with metal parts (for example during conveyance) and, as a result, themercury remains in a pure state and does not form any amalgam. This is conducive to the quality of the gaseous filling. 50

The arrangement insofar as described hereinabove is still incomplete however. It is not applicable as such for rectifiers for multiphase alternating current of high voltage because as mentioned already in the introduction of the d scription it often occurs that no discharge is struck to one or more of the anodes.

However, it has been found possible to arrange incandescent cathode rectifiers with mercury vapour formultiphase rectification. For this purpose conducting members are arranged between the anodes and the cathode either outside on the tube wall or in the interior of the tube. These conducting members, which may be composed for example of a strip of metal foil, are designated in Figure l by 9 and are electrically connected to the anodes. If they are enclosed Within the space of discharge as shown in Figure 3 by Hi, this connection is preferably established by means of a condenser I l. If arranged outside on the tube wall, the members may be connected directly to the corresponding anodes. On the drawing they are shown to make contact with the leading-in wires of the anodes. In this case they may be constituted e. g. by strips of aquadag or conducting paint that extend on the outer wall of the arms 6 in the direction of the path of discharge. If the mercury vapour filling under constant pressure is combined with the presence of conducting members as referred to before, an excellent rectifier is obtained which may be made for multiphase current of high voltage and shows a uniform action, the life of this rectifier being increased to a high extent owing to the mercury filling.

The use of a mercury reservoir separately connected to the tube also permits the pressure in the tube to be regulated at will. This may, indeed, be effected by making the mercury in the reservoir assume a certain temperature corresponding to the value of the desired vapour pressure. For this purpose an electric heating element I!) may be used, the flow of current throughsame being regulated automatically or not so that the temperature of the mercury, and consequently the pressure in the valve, has a desired constant value. It is only natural that the object is not to raise the mercury to a temperature higher than that in the valve, and other heating means may obviously be used; if necessary, a cooling means may serve to give a desired value to the temperature of the mercury.

Figure 2 shows a tube similar to that of Figure 1, in which conducting members H are helically arranged on the arms 82. A mercury reservoir I3 is enclosed within the stem l4 and communicates with the interior of the tube through a capillary tube l5. Again an electric heating element I S is provided, the leading-in wires of which, together with those for the incandescent cathode, may for example be connected to contact pins fixed to a cap. The attachment to the stem of the valve eliminates the risk of the mercury reservoir breaking oif by a shock, which might be possible with the construction shown in Figure 1.

For the parts of the tube of Figure 3 which substantially corresponds with the tube of Figure 2 the same indicating figures are used. Moreover the figure shows a normal circuit diagram for rectifiers. The transformer i8 has two secondary windings I9 and 20, the first mentioned feeding the anodes of the rectifier and the second giving the heating current for the cathode 4. The middle points of the windings l9 and 20 are connected to the terminals 2| for the direct current load.

What I claim is:

1. An electric discharge tube adapted for rectifying multiphase alternating current, having a vitreous container, an incandescible cathode, a plurality of anodes, a gaseous filling comprising mercury vapor and metal members disposed between the cathode and the anodes, these members being electrically connected to the corresponding anodes, and a separate reservoir containing liquid mercury and located within a stem sealed to the container, and a capillary tube connecting the reservoir with the interior of the tube.

2. An electric discharge tube adapted for rectifying multiphase alternating current, having an incandescible cathode, a plurality of anodes and a gaseous filling comprising mercury vapor and another gas, metal members between the incandescible cathode and each of the anodes, said members being electrically connected to the corresponding anodes, said tube comprising a hollow stem and a reservoir containing liquid mercury within the stem and communicating with the interior of the tube through a capillary tube, and means for regulating the temperature of the mercury reservoir.

3. An electric rectifying tube comprising an envelope and a plurality of electrodes therein comprising at least one cathode and one anode, a hollow stem sealed to said envelope, and leadin wires for at least one of the electrodes passing through said stem, and a reservoir containing liquid mercury disposed within said stem, said reservoir communicating with the interior of said envelope.

4. An electric rectifying tube comprising an envelope, an anode and a cathode within said envelope, said envelope forming a discharge space around said anode and cathode, lead Wires for said anode and cathode, the lead wires to the cathode passing through the bottom of the envelope, seals for said lead wires, a reservoir disposed in the portion of the tube between the seal of the cathode lead wire and the bottom contour line of the envelope and being in restricted communication with the discharge space of the tube, and a quantity of liquid mercury Within said reservoir.

JOHANNES GIJSBERTUS WILHELM MULDER. 

